Our office received a phone call from our patient who said their implant crown was loose. The patient stated that the crown seemed loose for a few weeks, but since there was no pain or soreness, they did not call the office immediately.
While these types of calls are infrequent, they are alarming. The patient is unaware of the catastrophic nature of the potential outcome. A loose implant screw is straightforward, but the possibility of implant body fracture can be catastrophic with the resulting loss of the implant and surrounding bone. The “red flags” are raised and the patient is hurriedly placed into the schedule for examination.
Upon evaluation, the implant crown, was determined to be loose. The implant placement and crown fabrication were performed prior to this individual being a patient in my practice. The implant had been placed more than 20 years prior. The situation was a cemented crown and implant abutment. Access to the screw channel was made through the occlusal surface. Fortunately, the retaining screw was loose and the implant body itself appeared to be intact on radiographic review.
Implant screw loosening was a more common occurrence with older implant systems. As this was an externally hexed Branemark implant, the design did not favor single-unit restorations. The functional stresses placed upon the implant abutment connection can more easily result in retaining screw loosening and potential screw fracture. I have included some review articles below that address this issue.
While relieved that the implant fixture itself was solid, I was concerned with the stability and the continuity of the hex connection. There was potential that the extended period of crown mobility had damaged the connection.
The hex indexes of dental implants are a key component to stability and alignment of the final restoration The hex provides the anti-rotational resistance needed to maintain the restoration positioning. If the retaining screw should loosen, the subsequent micro-movement of the restoration may cause damage to the surface and angles of the hex.
Continued mobility may cause abrasion and attrition to a degree that the anti-rotational connection is no longer resistant. It is important to determine the hex continuity prior to replacing the restoration. Restoration longevity and predictability are greatly reduced if significant wear has occurred.
Evaluation of the continuity of the hex is imperative prior to replacing or restoring the implant restoration. Internal hex implants will be more difficult to evaluate than external hex systems. Visual inspection is important, but it can be very challenging to observe minor and subtle faceting that may have occurred at the corners of the hex.
Magnification is paramount. The higher the magnification the better. But even at high magnification, it can be challenging to visually navigate the “tunnel of tissue” that exists as normal biology around the implant fixture. The sightline can be dark and obscured. Attempting to use intra-oral cameras or scanners as tools to evaluate the implant may be possible, but due to the inadequate light penetration, visibility is reduced.
A simple “analog style” implant impression technique may be utilized to overcome this situation. The technique involves using a silicone bite registration material to capture the hex as a negative reflection for inspection.
I recommend using a bite registration material over polyvinyl siloxane. The viscosity of the polyvinyl material may get lodged into the screw channel and could affect proper torque of the final retention screw. Additionally, the setting time is more extended with the polyvinyl materials.
In this situation an implant fixture packaging sleeve was utilized as the “impression tray.” The diameter of the sleeve allowed access into the first molar implant area. Tray adhesive was applied to the inner aspect of the sleeve to adhere the registration material.
For index impression, the implant body was dried with an air syringe. The bite registration material was injected into the packaging sleeve and directly onto the head of the implant. Once the registration material was set, it was removed and inspected.
The implant hex was captured perfectly in the bite registration impression. The hex continuity could be easily examined for faceting or defectiveness. Fortunately, in this case, the hex was not damaged from the prolonged micro-movement of the loose abutment and crown. The patient was then scheduled for the restoration replacement.
Loose implant crowns can create significant anxiety for both dentists and patients. The micro-movement associated with the mobile restoration has the potential to affect the continuity of the hexagonal attachment, reducing the stability of the final restoration.
This implant impression technique described provides for definitive observation of the integrity of the hex. This “impression tool” can function as a reliable record of the implant connection.
Jeffrey Bonk, D.D.S., is a member of Spear Resident Faculty.
Literature review: Screw loosening; External vs. Internal hexed implant design
Schwarz, Melvyn S. "Mechanical complications of dental implants." Clinical Oral Implants Research: Chapter 10 11 (2000): 156-158.
Khraisat, Ameen, et al. "Abutment screw loosening and bending resistance of external hexagon implant system after lateral cyclic loading." Clinical implant dentistry and related research 6.3 (2004): 157-164.
Simon, Robert L. "Single implant-supported molar and premolar crowns: a ten-year retrospective clinical report." The Journal of prosthetic dentistry 90.6 (2003): 517-521.
Ceruso, F. M., et al. "Implant-abutment connections on single crowns: a systematic review." ORAL & implantology 10.4 (2017): 349.
Literature review: Implant connection wear and abrasion
Fretwurst, Tobias, et al. "Metal elements in tissue with dental peri-implantitis: a pilot study." Clinical oral implants research27.9 (2016): 1178-1186.
Fretwurst, T., et al. "Is metal particle release associated with peri-implant bone destruction? An emerging concept." Journal of dental research 97.3 (2018): 259-265.
Nelson, Katja, et al. "The Impact of Force Transmission on Narrow-Body Dental Implants Made of Commercially Pure Titanium and Titanium Zirconia Alloy with a Conical Implant-Abutment Connection: An Experimental Pilot Study." International Journal of Oral & Maxillofacial Implants 31.5 (2016).